#include <fstream>
#define N 1000010
using namespace std;
ifstream f("fractii.in");
ofstream g("fractii.out");
int n,p[N],e[N];
void ciur(int,int*);
long long sol;
int main()
{
    int x,i,j,k;
    f>>n;
    ciur(n,p);
    sol=1;
    e[1]=1;
    for(i=2;i<=n;i++)
    {
        j=i;
        k=p[j];
        x=k-1;
        j/=k;
        while(j%k==0)
        {
            x*=k;
            j/=k;

        }
        e[i]=x*e[j];
        sol+=2*e[i];

    }
    g<<sol;
    return 0;
}
void ciur(int n,int *p)
{
    int i,j,k;
    for(i=2;i<=n;i+=2)
        p[i]=2;
    for(i=3;i*i<=n;i+=2)
        if(!p[i])
        {
            p[i]=i;
            for(j=i*i,k=2*i;j<=n;j+=k)
                p[j]=i;
        }
    for(;i<=n;i+=2)
        if(!p[i])
            p[i]=i;
}